Objective:
To elucidate the double supply of blood to the primary motor speech area
(Broca’s area) and provide the Morphometric data of collateral
circulation to this area.

Subject and methods:
A total number of 100 cerebral hemispheres were obtained from cadavers
and put in 10 percent formalin for one week so as to fix them. A mixture
of gelatin and Indian ink of various colours was injected in ACA, MCA
and PCA separately. Measurement of length and diameter of each vessels
was made by digital vernier caliper.

Results:
The middle cerebral artery was the major artery supplying this area
while the collosomarginal artery appear as collateral artery in
significant cases and this double supply to this area could be the cause
of better outcome of cerebral infarcts of this area.

Conclusion:
Itcould explain the better survival rates in cerebral ischemia
of this area.

The collateral vessels may modify the effects of cerebral ischemia. There is
usually not enough redundancy in the blood vessels of the brain to support
function if one vessel is suddenly occluded. Many smaller penetrating brain
vessels as the lenticulostriate branches of MCA that supply the basal
ganglia and internal capsule, as well as the penetrating branches from
vessels on the brain surface that supply deep white matter, are terminal
arteries. This means that they form few if any connections with other
arteries. When they are occluded, the brain regions they supply will
therefore become ischemic. Other vessels form anastomoses that potentially
could protect the brain from infarction, or limit the amount of damage, by
providing alternative routes for blood flow1.

Motor speech area (Broca’s area 44 & 45) is situated in pars traingularies
and opercularis of the inferior frontal gyrus in the dominant hemisphere
(left hemisphere in right handed and right hemisphere in left handed
persons). It is a centre for initiation of speech as it plays the essential
role in movements of tongue, lips and larynx. A lesion of this area results
in “motor aphasia”2.

In a comparative study on variety of animals, the hemispheres
were divided into well defined lobes. The anterior frontal lobes were
honored as the seat of man’s highest intellectual faculties and sensation.
Language was considered as faculty to establish a constant relation between
ideas and signs and the ability to articulate was placed in the posterior
part of the 3rd frontal convolution of the left hemisphere. The
identification of the seat of motor speech was followed slightly more than a
decade later by the cerebral injury responsible for sensory aphasia. This
discovery interrelated the written aspects of communication in the occipital
cortex with auditory aspects in Wernick’s area in the temporal lobe and
motor expression in Broca’s area in the temporal lobe adjacent to the
laryngeal area of the motor cortex3.

Attempts to understand the varied structure-function
relationships within the human brain have a long history. Through the use of
variety of techniques including analysis of behavioral and cognitive change
due to brain injury and a variety of staining techniques, function maps of
the brain have been built up over many years providing the neurological
basis for functional specialization of the cerebral arteries and other brain
structures. In the 1980’s positron emission tomography (PET) which measures
function related changes in regional cerebral blood flow, closely followed
in early 1990’s by functional magnetic resonance imaging (MRI) which
measures blood oxygen level dependent signals revolutionized the field.
These techniques brought noninvasive high-spatial resolution approaches to
brain structure-function studies for the first time enabling measurement of
region specific changes of brain activity correlated with particular
cognitive, motor or sensory tasks4.

The variations in the frontal lobe artery resulted in tonic and
colonic seizures due to a focus in the left frontal region where blood was
supplied by the contra lateral fronto-orbital artery. The region was
vulnerable to ischemic changes due to decreases in blood supply5.

The middle cerebral artery was found to supply the cortical
areas in the territory of the orbitofrontal and prefrontal arteries. The
anterior temporal lobe and the anterior frontal lobe are supplied by the
duplicated MCA and accessory MCA respectively. The development of the
duplicated MCA and accessory MCA is an anomalously early ramification of the
early branches of the MCA6.

Two cases of acute embolic occlusion of the internal carotid
artery and the middle cerebral artery in association with a patent accessory
MCA described that the frontal lobe was salvaged to some extent did not
provide sufficient collateral blood supply to the MCA territory to spare
rest of the frontal lobe7.

Language has been linked to the Broca’s area since Paul Peirie
Broca’s reported impairments in two patients. They had lost the ability to
speak after injury to the posterior inferior frontal gyrus. Since then, the
approximate region he identified has become known as Broca’s area, and the
deficit in language production as Broca’s aphasia8.

MATERIAL AND METHODS

It was cross sectional analytical study conducted at the Post Graduate
Medical Institute Lahore. Hundred embalmed and non-embalmed human brains
were collected from recently deceased adult males between twenty to sixty
years of age from various teaching institutes, forensic department KEMU
Lahore and Anatomy departments of SIMS, KEMU, FJMC, and AIMC with
permission.

Skull cap was cut by electric saw passing through middle of
frontal bone, squama of the temporal bone and the occipital bone. Skull cap
was removed. After incising the falx cerebreri and tentorium cerebrelli hand
was passed over the surface of brain and it was removed through epidural
space without any injury to the blood vessels compression on the brain.

Each brain was examined for any bleeding, softening or any other
pathological lesion like infarcts and specimens with these lesions were
excluded. Then each selected brain was put in 10% formalin jar for one week
so that it got fixed.

After one week dura was removed gently by forceps and
intravenous branula no.24 was passed into each anterior, middle and
posterior cerebral artery separately at different times. An injection medium
consisting of mixture of gelatin with undiluted blue Indian ink was injected
by syringe into anterior cerebral artery after legating anterior
communicating artery. After injection the branula was remove and ligature
applied to the artery so that the dye may not escape. Now the branula was
passed in the middle cerebral artery and an injection medium consisting of
mixture of gelatin with undiluted Red Indian ink was injected and ligature
applied to the artery. The contrasting colours clearly demarcated the blood
vessels supplying the functional areas of the brain.

Each brain was examined for any bleeding, softening or any other
pathological lesion like infarcts and specimens with these lesions were
excluded. Then each selected brain was put in 10% formalin jar for one week
so that it got fixed.

After one week dura was removed gently by forceps and
intravenous branula no.24 was passed into each anterior, middle and
posterior cerebral artery separately at different times. An injection medium
consisting of mixture of gelatin with undiluted blue Indian ink was injected
by syringe into anterior cerebral artery, middle cerebral artery and
posterior cerebral artery separately.

As the vessels of the brain were torturous it was difficult to
measure their length by digital caliper, so a flexible copper wire was
molded along the course of each vessel. The wire was cut according to the
length of the vessel and straightened out and actual length of the vessel
was computed on the digital caliper.

The diameter of the blood vessel was computed by digital
electronic vernier caliper. The external diameter of each vessel was
measured at proximal, middle and distal compartments. The mean diameter was
noted for statistical analysis.

RESULTS

Gross Distribution of vessels:
The frontal artery branch of superior trunk of MCA was found to be the major
source of blood supply to the Broca’s area as it was present in all hundred
cases while the callosomarginal artery branch of pericallosal artery a
branch of ACA appeared as dual blood supply to Broca’s area in 4 cases (4%).

The Frontal Branch of MCA (Table 1):
First we studied the frontal branch of MCA. Out of 100 cases it originated
from the superior trunk of MCA in all cases (100%). It showed a nodular
surface in 41 cases (41%). In another 59 cases (59%) it appeared smooth. It
originated near lateral sulcus of cerebral hemisphere and passed over the
inferior frontal gyrus with straight course in 68 cases (68%). It followed a
torturous forward course in 32 cases (32%). It terminated into 1 to 2
cortical branches. Its maximum and minimum diameters at proximal segment
were 1.36mm and 1.24mm respectively. Its average diameter at proximal
segment was 1.30mm. its maximum and minimum diameters at central segment
were 1.26mm and 1.16mm respectively. Its average diameter at central segment
was 1.21mm. Their maximum and minimum diameters at distal segment were
1.12mm and 1.04mm respectively. Its average diameter at distal segment was
1.08mm. its mean diameter was found to be 1.19±0.02mm.ts mean length was
noted to be 9.6mm±0.22mm. the mean diameter of its cortical branches was
1.02mm±0.03mm.

The Callosomarginal Artery (Table 2):
The callosmarginal artery out of 100 cases was found to supply the Broca’s
area in 4 cases (4%) as collateral (additional) vessel. It was found to
originate from pericallosal artery in 3 cases (75%). In another 1 case (25%)
which originate from ACA. It surface was found to be smooth in 2 cases
(50%). While in other 2 cases (50%) it appeared beaded. It followed
torturous course in 1 case (25%). In other 3 cases (75%) it followed
straight course. Its maximum and minimum diameters at proximal segment were
1.53mm and 1.42mm respectively. Its average diameter at proximal segment was
1.47mm. Its maximum and minimum diameters at central segment were 1.35mm and
1.24mm respectively. It average diameter at central segment was 1.29mm. Its
maximum and minimum diameters at distal segment were 1.26mm and 1.15mm
respectively. Its average diameter at distal segment was 1.20mm. Its mean
diameter was found to be 1.32±02mm. its mean length was noted to be
17.6mm±0.22mm. It terminated in to 1 to 2 cortical branches. The means
diameter of its cortical branches was 1.04mm±0.05mm.

Table 1: Morphometric variables of the Frontal Branch of MCA artery:

Origin (n=100)

Surface

Course

Mean

Mean

ACA

Nodular

Smooth

Straight

Curved

Diameter(mm)

Length(mm)

100

41 cases (41%)

59 (59%)

68 (68%)

32 (32%)

1.19±0.02

9.6±0.22

Table 2: Morphometric variables of the callosomarginal artery

Origin

Surface

Course

Mean Diameter

Mean Length

From pericallosal artery

From ACA

Nodular

Smooth

Straight

Curved

Diameter(mm)

Length(mm)

3 cases (75%)

1 (25%)

2 (50%)

2 (50%)

3 (75%)

1 (25%)

1.32±02

17.6±0.22

DISCUSSION

Duplication of middle cerebral artery and one accessory middle cerebral
artery were studied in two patients and it was noted that the double
vascularization of the hemisphere can give rise to strokes with a better
progression and prognosis despite the occlusion of one of the middle
cerebral artery9. In our study 4 cases (4%) of
collateral blood supply to the Broca’s area was provided by callosomarginal
artery. It was described that an accessory middle cerebral artery arises
from the anterior cerebral artery and go to a territory usually supplied by
the middle cerebral artery. This occurred in 3% of 347 cases10.
In our study the incidence of callosomarginal artery was 4% of 100 cases.

In an another study11 on the variations of anterior and middle
cerebral arteries it was found in 65% cases, the path is arch shaped but in
44% it is straight and oblique in direction while in 1% the pre communicant
segment of anterior cerebral artery it has wavy path. The results are
comparable to our study.

In another study12 one accessory MCA and the early branches were
given off before the perforators in two middle cerebral arteries, making an
incidence of anomalies of 3%. There was no aneurysm. The results are
comparable to our study.

Two right-handed patients with clinical evidence of major infarction in the
territory of the left anterior cerebral artery developed a profound but
transient aphasia characterized by (1) a striking dissociation between
intact repetition and grossly disturbed spontaneous conversational speech,
(2) an absence of phonemic paraphasia, (3) a lack of speech inhibition and
(4) relative preservation of conformation naming and comprehension. Despite
the initially profound motor aphasia, serviceable spontaneous conversational
speech returned in two to three months. In fact there may have been damage
to the pre-motor area (particularly the supplementary motor region), an area
that has been shown to play a role in the initiation, continuation and
inhibition of speech13. These results show involvement of
anterior cerebral artery in supplying the motor speech area. In our study
the callosomarginal artery branch of ACA appeared as collateral supply to
the motor speech area.

MCA strokes involve the territory of face and upper limb with aphasia. Their
incidence increases with age. This shows involvement of the primary motor
area and Broca’s area. It causes contra lateral hemiplegia14. In
our study also MCA branches are found to nourish these areas.

Clinical, radiological and pathological studies in patients with stroke,
presenting with pathological laughter as heralding manifestation, have shown
lesions in the internal capsule and thalamus, basal ganglion, hypothalamus
and ventral pons. In this report a patient with similar manifestation and
having a cortical infarct in the territory supplied by superior division of
middle cerebral artery15.

CONCLUSION

The middle cerebral artery as described in conventional studies is the major
source of blood supply to the Broca’s area is found to be the major supply
to this area in our study while the callosmarginal artery was found in 4%
cases to be collateral artery to this area in our study which could explain
the possible variable out come of cerebral infarcts with better progress in
dual blood supply.